A method of determining a concentration of plastic or other material not dissolved by silicon etchants contaminating a silicon product comprising: obtaining a sample of the silicon product contaminated with the plastic or other material not dissolved by silicon etchants; placing the sample of the silicon product into a ultrasonic bath liquid to produce a slurry comprising the ultrasonic bath liquid, silicon dust, and the plastic or other material not dissolved by silicon etchants; filtering the slurry with a first filter to produce a cake comprising the silicon dust and the plastic or other material not dissolved by silicon etchants separated from the sample of the silicon product; and analyzing the cake to determine the concentration of plastic or other material not dissolved by silicon etchants contaminating the silicon product.